stiletto 2 car kit having an issue.

Hey, I have been having this problem since I bought the radio and the car kit about three months ago. When I am play recorded music in the car with the radio docked and the power IS NOT Plugged in, I can control the volume of the radio and turn it all the way down. (because I am using a cassette adapter and you have to have the radio volume really low and turn the speakers up to get the best clarity). But when the radio is docked and THERE IS power going to the radio from the cigarette lihghter, I cont make the volume go all the way doen ON THE RADIO (with the solver buttons on the radio itself) making the quality a little staticky. So the radio has 2 different volume controls one when its not recieving power (the better one cause I can turn the volume down) and when it is recieving power (not ideal cause its lowest volume setting is too loud and I gat static)
I call tech support and after a half hour, I realized the guy couldent help me. Can someone on here?